The present invention relates to telecommunications in general, and, more particularly, to a technique for setting up a wireless telecommunications call across a regional or political boundary.
FIG. 1 depicts a schematic diagram of a portion of a typical wireless telecommunications system in the prior art, which system provides wireless telecommunications service to a number of wireless terminals (e.g., wireless terminals 101-1 through 101-3) that are situated within a geographic area. The heart of a typical wireless telecommunications system is Wireless Switching Center (xe2x80x9cWSCxe2x80x9d) 120, which is sometimes also known as a Mobile Switching Center (xe2x80x9cMSCxe2x80x9d) or a Mobile Telephone Switching Office (xe2x80x9cMTSOxe2x80x9d). Typically, Wireless Switching Center 120 is connected to a plurality of base stations (e.g., base stations 103-1 through 103-5) that are dispersed throughout the geographic area serviced by the system and to the local and long-distance telephone and data networks (e.g., local-office 130, local-office 138 and toll-office 140). Wireless Switching Center 120 is responsible for, among other things, establishing and maintaining calls between wireless terminals and between a wireless terminal and a wireline terminal (e.g., wireline terminal 150), which is connected to the system via the local and/or long-distance networks.
The geographic area serviced by a wireless telecommunications system is partitioned into a number of spatially distinct areas called xe2x80x9ccells.xe2x80x9d As depicted in FIG. 1, each cell is schematically represented by a hexagon; in practice, however, each cell usually has an irregular shape that depends on the topography of the terrain serviced by the system. Typically, each cell contains a base station, which comprises the radios and antennas that the base station uses to communicate with the wireless terminals in that cell and also comprises the transmission equipment that the base station uses to communicate with Wireless Switching Center 120.
For example, when wireless terminal 101-1 desires to communicate with wireless terminal 101-2, wireless terminal 101-1 transmits the desired information to base station 103-1, which relays the information to Wireless Switching Center 120 over wireline 102-1. Upon receipt of the information, and with the knowledge that it is intended for wireless terminal 101-2, Wireless Switching Center 120 then returns the information back to base station 103-1 over wireline 102-1, which relays the information, via radio, to wireless terminal 101-2.
Because a wireless terminal is mobile, it can be served by different base stations as it moves. In fact, if a wireless terminal moves a substantial distance it can be serviced by another wireless switching center and its satellite base stations rather than by the wireless terminal""s xe2x80x9chomexe2x80x9d wireless switching center.
For example, FIG. 2 depicts a flowchart of a method in the prior art, which involves the interaction of three wireless switching centers (calling WSC 201, visiting WSC 202 and home WSC 203) and two wireless terminals (wireless terminal 211 and wireless terminal 212) as a call is established from wireless terminal 211 to wireless terminal 212.
Calling WSC 201, visiting WSC 202 and home WSC 203 are each conventional wireless switching centers as well-known to those skilled in the art. In the example in FIG. 2, calling WSC 201 and visiting WSC 202 are in the same region (or country) and both are in a different region (or country) than is home WSC 203. For example, calling WSC 201 and visiting WSC 202 might be in northern Illinois and home WSC 203 might be in Seoul, Korea.
For the purposes of this specification, the word xe2x80x9cregionxe2x80x9d is defined as one or more geographic areas that are: (1) owned or operated by the same entity, or (2) administered by the same regulatory body. For the purposes of this specification, the word xe2x80x9ccountryxe2x80x9d is defined as a primary political unit (e.g., the United States, Canada, the United Kingdom, Japan, etc.) or a subprimary political unit (e.g., New Jersey, Alberta, Wales, Okinawa, etc.).
Wireless terminal 211 is a conventional wireless terminal that is currently served by calling WSC 201. It is irrelevant to whether wireless terminal 211 is being served by its home wireless switching center or is roaming and being served by another wireless switching center.
Wireless terminal 212 is a conventional wireless terminal whose home wireless switching center is home WSC 203. Therefore, home WSC 203 has associated with it a home location register or xe2x80x9cHLRxe2x80x9d (not shown) that maintains a database that includes the identity of the wireless switching center that is serving wireless terminal 212 at any given time when wireless terminal 212 is roaming.
When wireless terminal 211 desires to place a call to wireless terminal 212, it begins at step 231 by placing the call via calling WSC 201. As part of step 231, wireless terminal 211 provides an indicium (e.g., the telephone or directory number, etc.) of the identity of wireless terminal 212 to calling WSC 201 so that calling WSC 201 can determine how and where to direct the call. Calling WSC 201 analyzes the indicium, in well-known fashion, to determine that the home wireless switching center of wireless terminal 212 is home WSC 203.
Therefore, at step 232, calling WSC 201 transmits a call set-up message to home WSC 203 to indicate that calling WSC 201 desires to establish a call with wireless terminal 212, whom both calling WSC 201 and home WSC 203 know has home WSC 203 as its home wireless switching center. Typically, the call set-up message from calling WSC 201 to home WSC 203 comprises: (1) an indicium (e.g., the telephone or directory number, etc.) of the identity of wireless terminal 201 (e.g., for caller ID purposes, for billing purposes, etc.), and (2) an indicium (e.g., the telephone or directory number, etc.) of the identity of wireless terminal 202 (for routing purposes).
As part of step 232, home WSC 203 queries its home location register and determines that wireless terminal is currently being served by visiting WSC 202.
Therefore, at step 233, home WSC 203 transmits another call set-up message to visiting WSC 202 to indicate that calling WSC 201 desires to establish a call with wireless terminal 212.
Upon receipt of the call set-up message, visiting WSC 202 completes the call at step 234 to wireless terminal 212 so that wireless terminal 211 and wireless terminal 212 can communicate. Although wireless terminal 211 and wireless terminal 212 might be only a few miles apart, the call between them crosses a regional or political boundary twice! Therefore, if there are tariffs or surcharges on calls crossing regional or political boundaries the call between wireless terminal 211 and wireless terminal 212 could be horrendously expensive. Furthermore, large long-distance charges could apply for the call. Therefore, the need exists for reducing the tariffs, surcharges and long-distance charges that might be incurred for calls involving wireless switching centers in multiple regions (or countries).
Some embodiments of the present invention are capable of reducing, or even eliminating, the tariffs, surcharges and long-distance charges that might be incurred for calls involving wireless switching centers in multiple regions (or countries). This is accomplished in the illustrative embodiment by trunking calls directly from the calling wireless switching center to the visiting wireless switching center, where advantageous, without trunking the call across a regional or political boundary, as is done in the prior art.
The illustrative embodiment of the present invention comprises: receiving at a first wireless switching center a first call set-up message from a second wireless switching center; transmitting, in response to the first call set-up message, a second call set-up message from the first wireless switching center to a third wireless switching center; receiving, in response to the second call set-up message, a first call set-up response message at the first wireless switching center from the third wireless switching center; and transmitting, in response to the first call set-up response message, a call set-up response message from the first wireless switching center to the second wireless switching center directing the second wireless switching center to set-up a call directly with the third wireless switching center.